1. Field of the Invention
The invention relates to an ultrasonic probe and a method for the nondestructive testing of a planar test specimen, such as a pipe wall, a slab, or a plate, which provides a plurality of ultrasonic transducer segments, which are activatable individually or in groups by means of phased array technology for the emission of ultrasonic plate waves having a predefinable propagation direction in the test specimen to be tested.
2. Description of the Prior Art
Ultrasonic probes of the above-mentioned species are used, for example, in the nondestructive testing of extended test objects, in order to detect cracks or other types of material defects in test specimens or test specimen walls. In particular in the examination of weld seams, the ultrasonic waves are incident at an inclined angle relative to the weld seam as much as possible, in order to detect weld seam defects either in a reflection, diffraction, or transmission measurement in this manner.
In addition to the incidence of the ultrasonic signals in a test specimen wall to be studied at a permanently predefined incidence angle, due to which it is necessary to move the ultrasonic probe used for this purpose relative to the weld seam to register the entire weld seam geometry, ultrasonic probes are known and are in use which, based on the phased array technology, allow a variation of the incidence angle of the ultrasonic waves during the testing. Using this electronic pivoting technique, during which the main propagation direction of the ultrasonic wave field which can be coupled into the test specimen is pivoted, probe movements in the direction of the weld seam can be omitted or minimized, whereby nondestructive ultrasonic examinations on test specimens can be performed more rapidly and therefore more cost-effectively.
Ultrasonic probes, which are also referred to as phased array probes, which are suitable for the use of the phased array technology, consist of a plurality of individually activatable ultrasonic transducer segments, which generate ultrasonic waves. The individual segments, which generate ultrasonic waves are combined to form a phased array probe, are differently activated in the case of transmission or differently read out in the case of reception. In most cases, the differing activation of the individual segments is performed by individual amplitude and/or phase configuration or by a time-delayed activation, in order to achieve an angular incidence or focusing of the ultrasonic wave field, which results through superposition of the individual fields originating from the ultrasonic transducer segments and which is emitted as a whole by the phased array probe.
In spatially delimited test specimens to be studied, for example, plates or plate-shaped test specimens, so-called ultrasonic plate waves can form, whose propagation direction is oriented parallel to the plate surface and whose ultrasonic wavelength is of the magnitude of the plate thickness. In addition to classical piezoelectric angle probes, electromagnetic ultrasonic transducers can also be used for the excitation and reception of such ultrasonic plate waves, during which a selective excitation of selected plate wave modes and also plate waves having an SH polarization are possible. The latter relates to shear waves, which are polarized parallel to the wall surface. Therefore, these waves can also be referred to as “horizontally polarized shear waves” or, for the case of plate waves, as “horizontally polarized plate waves”.
In order to set a specific incidence direction in a voluminously extended test specimen, the known phased array technology can be used. Segmented ultrasonic probes are used, which can be activated in a phase-oriented manner using suitable electronics. This approach can also be used for the excitation of ultrasonic plate wave modes. It is thus possible, if the emission direction of the segments is aligned perpendicularly to the linear arrangement of the segments, to rotate the emission direction of the ultrasonic summation signal through a phase-oriented activation in the plate plane. See P. Wilcox, M. Lowe, and P. Cawley: Lamb and SH Wave Transducer Arrays for the Inspection of Large Areas of Thick Plates, in Review of Progress in QNDE 2000, 19, pages 1049-1056. However, it is problematic that the pivot range of the ultrasonic wave field is limited by the aperture width of each individual ultrasonic transducer segment.
The publication DE 10 2004 063 482 B3 describes an arrangement for the incidence of US shear waves into a tubular or slab-shaped ferromagnetic test specimen for the crack testing thereof. Both the emission and also the reception of the US shear waves are performed with the aid of an HF coil arrangement, which is attached to a probe, which is pre-magnetized in the area of the HF coil arrangement.
DE 10 2004 053 584 A1 discloses nondestructive material testing utilizing of ultrasound, in which EMUS transducers are used to generate ultrasonic waves which can be emitted into the test specimen perpendicular to the test specimen surface.
Finally, DE 10 2008 002 394 A1 describes a universal ultrasonic probe for the emission of ultrasonic waves which propagate within a test specimen parallel to the test specimen surface, predominantly for studying welding melt zones. The probe is ring-shaped and has segmented separate regions for the emission and the reception of ultrasonic waves.